There is no need to disable Avast when installing new applications.
You don't have to uninstall/install. You can start Avast again in the on-access control panel.
If you have a problem, provide as much relevant details as possible.
- What OS? (version, service packs etc)
- What exact version of Avast?
- What have you already done trying to solve it?
- Do you get an error? If so which exact one?
- Is there an error in Avast's log file? If so which exact one?
etc etc.